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Parallel Circuits - Inductive

Inductance is measured in units of "henries" and the amount of opposition to current flow the inductive reactance is measured in units of "ohms" The following formula is used to calculate the inductive reactance:

where;

f = frequency in hertz L = inductance in henriesp = 3.1416

Voltage across and current through an inductor are described by Ohm's Law for inductors:

Find the current flow in the circuit with the pure inductor shown.

First finding the inductive reactance as:

Remember, current in an ac circuit with pure inductance and negligible resistance will lag the voltage by 90 degrees. The figure below shows the current and voltage waveforms for a pure inductance circuit. This can also be expressed in what is called "phasor" form which is the use of vectors math. This is done to keep track of the fact that the inductive reactance value in ohms will be out of phase with any resistance value in a circuit so the inductive reactance ohms and resistance ohms cannot be directly added together.

The counterclockwise position of the current from the voltage is a convention to show the current lagging the voltage.

The total reactance of several inductances in parallel can be obtained by the following rule.

For parallel circuits:

For a parallel circuit with 3 inductive reactances of 10, 20, and 30 ohms, the total inductive reactance is calculated as follows: